The invention relates to an acceleration monitoring method for a longitudinal dynamics open-loop or closed-loop controller in motor vehicles, in which an actual acceleration value is compared with a desired acceleration value, a defective operating condition of the motor vehicle being detected when the actual acceleration value is situated outside an error corridor including the desired acceleration value.
In conventional speed control systems, speed thresholds and/or acceleration thresholds are used to detect defective operating conditions. These threshold values are fixed in this case and set in an unchangeable fashion. A defective or impermissible response of the vehicle is detected and the active control operation is terminated when, without intervention by the driver, the vehicle speed departs by a specific measure from the desired speed or, in the case of acceleration, when an impermissible acceleration or retardation is reached.
In the case of control devices which set both the distance and the speed of a vehicle, the speed thresholds cannot be used in the situations in which the distance controller is active. Use is made for such devices of fixed acceleration thresholds, but these must be set such that they are already situated in the safety-critical retardation range. However, this means for the safety concept of the vehicle that some defects cannot be detected until there is a very strong effect on the handling performance of the vehicle, and this leads to impermissible critical driving situations.
It is the object of the invention to specify an acceleration monitoring method in the case of longitudinal dynamics closed-loop control in motor vehicles in the case of which critical driving situations are detected as quickly as possible.
This object is achieved according to the invention wherein error corridor is set in a variable fashion as a function of the current handling performance of the motor vehicle.
The advantage of the invention consists in the fact that errors or impermissible deviations are already detected when the effects on the handling performance are still slight. This is possible in a simple way by virtue of the fact that relative or dynamic acceleration thresholds are used for the monitoring instead of absolute and fixed ones, as previously.
In a development, the error corridor of the acceleration is adapted dynamically to the handling performance of the motor vehicle. Owing to the use of an error corridor, slight deviations in the acceleration value do not lead to intervention in the control.
In a simple design, the error corridor is set as a function of the speed of the vehicle to be controlled.
Alternatively, the error corridor can be varied as a function of the actual acceleration value and/or the desired acceleration value. In both cases, it is possible to react quickly to changes in the driving dynamics of the motor vehicle. Moreover, safety-critical situations can be taken into account more individually. Thus, in the case of high vehicle speeds the range of the desired acceleration value can be selected to be narrower than in the case of lower speeds.
The active control operation of the longitudinal dynamics closed-loop controller of the motor vehicle advantageously goes into an error mode when the actual acceleration value is situated outside the error corridor typifying the desired acceleration value. For reasons of safety, the brakes, engine and drive train go into an emergency operating mode, whereas the control of speed and/or distance are terminated.
In a development of the invention, the desired acceleration value is determined in a first vehicle dynamics system of the vehicle, and the determined desired acceleration value is output to the vehicle for the purpose of driving a second vehicle dynamics system thereof, which compares the determined desired acceleration value with the actual acceleration value and drives a speed-regulating control element of the motor vehicle as a result of the comparison.
The first vehicle dynamics system advantageously includes a distance controller for setting the distance of the vehicle to be controlled relative to a vehicle travelling in front, which controller determines the desired acceleration value from a distance to be set.
Thus, the desired acceleration value determined by the distance controller is used to drive a braking device of the motor vehicle, an electronic engine control or a drive train control or a gear control, thus releasing computing capacity in the said vehicle dynamics system.
In the case of the general use of a braking device of the motor vehicle, an electronic engine control or a drive train control or a gear control, it is possible for the driver to prescribe the desired acceleration value via an appropriate interface of these systems.